i can only comment to my car which is same as OP's, over 20k driven. and for sure agree with many points made..
the 15-50 is within owners manual
why not just buy the zinc mixed already with the oil? i assure you it is far better mixed than adding separately.
the Mobil 1 mentioned is one of the highest zinc content among brands without going full..xxx racing brand
my pressure at warm idle is about 30-35 psi. I drive below freezing occasionally and never at start up am i above 55psi.
synthetic vs dino? why not synthetic. i change about every 4-5k which usually is about one year. I add about 3 quarts in that time..

 

Yeah, RIGHT........


You are aware, aren't you, that the C-3 owners manual was written 50 years ago, back when all engines had "flat tappet cams", and all motor oils contained ZDDP, so it was a "no issue" situation.

 

if you just run synthetic and you dont increase the ZDDP and Zinc you risk flattening your cam and ruining your tappets.........

 

Another vote for Mobil One 15-50. High zinc, and good price and availability at your local Walmart.

 

Holly S. Batman! You add 3 quarts of oil in between changes?
WOW.
I also change oil about once a year, about 5K miles give or take. My dip stick shows I'm down a tad at oil change time. Like about 1/4 of a quart. I blame this on the minor leak I've had for years that I have never been able to stop.
if I was adding a quart to 1,500 miles. WOW, I'd have that apart!

 

I use only Redline synthetic and wix filters. They have a non racing 20-50 used it for 30 yrs great stuff..

 

i would say yes 2-3 quarts as an estimate..or adding while checking half quart at a time..
i am pretty sure valve seals letting by, no smoke past cold start.zero after that even full acceleration (visible anyway). I like the extra lubrication lol.. i drive 'spirited'

 

Good choice.

If your car is meeting your performance requirements, there is no reason to do anything. I've changed a valve spring with compressed air and the engine in the car. It's not fun. I couldn't imagine doing that 16 times, so the engine would have to come out. Certainly not worth it to (possibly) save the equivalent cost of 5 gallons of gasoline!

 

15W50 is a racing oil for use at the high oil temps encountered in racing. It is too heavy for use on the street. Many have the incorrect notion that heavier oil means heavy duty, which then gives better engine protection. The one and only issue is temperature. Oil thins out as it heats up, so the hotter the engine is while running, the heavier you want the oil to be at startup so that at the hotter running temp, it is still in the proper viscosity range. You could argue the exact numbers, but pretty much all engines want oil to be in the range of about 5-20 centistokes at whatever the oil temperature is in the engine. For a 15W50, that means oil temp should be in the range of about 220-300F before you run the engine hard. For a 5W30, that means oil temp range of about 170F-260F. A typical warmed up engine runs oil temp in the low 200’s on the street, might occasionally get to the mid 200’s if you are hot-rodding a bit on the street, but never gets to the upper 200’s unless you are doing hard core track driving, with extended periods of high power use.

At startup, all oils are too viscous. That’s why you take it easy until the engine is warmed up, and on the street, 15W50 is almost never hot enough to be in the ideal viscosity range of 5-20 centistokes. At 32F, viscosity for 5W30 and 15W50 are about 300 and 700, respectively. At 70F, those numbers have decreased to about 160 and 400. Even at 140F, both are still too viscous at about 50 and 90. For comparison, at room temperature the viscosities of syrup, cooking oil, and water are respectively about 1000, 50, and 1.

 

That or it could be a poor or no baffle in your valve cover and youre sucking oil into you pcv system....

 

Clearly you dont understand anything about oils or what they were used for when

15w50 oil is perfectly fine in cold temp and when the temp is naywhere 0c or colder about 2% of these cars are being driven. If any at all.
Secondly the mobil 1 15w50 is above 2000 ppm in zinc and phosphates which protect the flat tappet/ cam interface. They often will say they recommend it for old flat tappet engines.
Please stop giving bad advice without actually knowingvwhat you are talking about. You are only hurting our community

 

You have a Racer Brown flat tappet cam too, right?

Jebby

 

Just as clearly, you haven’t read my public profile. I’m a chemical engineer, retired from a major oil company, with plenty of experience with fuels, lubes, and engine testing of both. I understand your desire for zinc with flat tappets, and the 15W50 is indeed high in zinc. However, as I stated, 15W50 is too heavy for street use in most engines. If you are driving around on the street with an oil temp in the low 200’s, the oil is around 30 centistokes as it flows through your engine, which is thicker than desired for best engine wear rates. And even worse, it’s been thicker than a street viscosity oil for longer during the warm up period, which is where a substantial part of engine wear occurs. If you can’t find a high zinc oil in a reasonable street viscosity range, it would be better to use something like 5W30 or 0W40 plus some ZDDP additive as some in this thread have mentioned.

I should add a disclaimer. If an engine has very high clearances either by design or by wear, or if oil in those engines on the street typically runs very hot like mid 200's instead of low 200's, then the heavier oil might be appropriate. But the initial spec was for 30 weight as the upper weight number, so neither unusually high oil temp nor high clearance by design seem very likely to me. And unless the engine has been mistreated or is well past 100,000 miles, high clearance by wear also doesn’t sound likely. But since I don’t know the condition of, or oil temp in your engine, I don’t know for sure whether high clearances or high oil temp that would justify 15W50 exist.

 

What’s the concern about Frame oil filters?

 

The regular orange fram filters use a cardboard like substance as a filter, they clog easily, collapse and starve your engine...

 

Ya. Work in a building of engineers...had to put "push and pull" on the door handles to cut down on bruised forheads.. i could give a rats *** about your degree. Show me your engines, your time slips. What you have worked on lately. Show me a video of your motor making more than 2 hp per cube and show us a video of driving it. Ill post pics of the door stickers....the common sense of a dead house plant is what engineers that dont get out and use that big brain bring to the table.

Oh and centistokes boy....I did the 10-30 high zddp bit on my 427...clearly you havent read my.blah blah blah....you want to measure dicks son...you want me to start just ask partner. 10-30 in a high rev 427 last about 500 miles with no abuse using Clevite bimetal bearings

 

As for filter choice i like the K&N truck size filters..a lot more surface area, holds an extra quart...and it will trap the crap from torn up bearings

 

rr,
Calm down. What is your problem lately with all the bashing?

Take your dog for a walk. Join a Prius forum. Or go on a long vacation.
Good grief!

 

And a pleasant day to you too. I admit that I don’t have experience with highly modified engines putting out 2 HP per cube, and I’d also admit that the experience of someone who had built such an engine would be more valuable than mine for what oil would give best life in such an engine. But as far as I can tell from the thread, the OP has an unmodified 1979 L82. Big oil companies such as mine do extensive testing of both fuels and lubes in such engines with 50,000 mile controlled tests with subsequent teardown and inspection, so we know a bit more about what fuels and lubes work best in those engines than dead house plants do. Readers will have to decide for themselves whether such experience is enough greater than that of dead house plants for it to influence their thinking on oil for stock engines driven on the street.

 

Thank you for the introduction to centistokes — I had never heard that term before, so hit Google. Feel free to PM me your reply if you are willing to answer but do not wish to do it here. Alternatively, a link to a website explaining in layman's terms would suffice.

Does a multi-grade oil exhibit the characteristics of all of the weights in its range depending on temperature it's being subjected to? For example, will a 15w-50 behave like a 30 weight at moderate engine temperatures and only behave with the 50 weight characteristics when the temps reach 200°+? Is it like a sliding (no pun intended) scale of characteristics from cold start to full operating temp? If it is a continuous variability, wouldn't a 15w-50 and a 10w-30 show the same characteristics at 200° and only become distinct above that where the 10w-30 would fail?